Fix improper initialization order for readline.

Turns out we must set rl_basic_word_break_characters *before* we call
rl_initialize() the first time, because it will quietly copy that value
elsewhere --- but only on the first call.  (Love these undocumented
dependencies.)  I broke this yesterday in commit 2ec477dc;
like that commit, back-patch to all active branches.  Per report from
Pavel Stehule.